Patients with kidney failure or partial kidney failure typically undergo hemodialysis treatment in order to remove toxins and excess fluids from their blood. To do this, blood is taken from a patient through an intake needle (or catheter) which draws blood from a vessel such as an artery located in a specifically accepted access location (for example, an arm, thigh, subclavian, etc.). The needle (or catheter) is connected to extracorporeal tubing that is fed to a peristaltic pump and then to a dialyzer which cleans the blood and removes excess water. The cleaned blood is then usually returned to the patient through additional extracorporeal tubing and another needle (or catheter). (In some cases, the blood may be returned to the body through the same extracorporeal connections as the intake—a mode called “single needle dialysis”). Sometimes, a heparin drip is located in the hemodialysis loop to prevent the blood from coagulating. By way of background, as the drawn blood passes through the dialyzer, it travels in straw-like tubes within the dialyzer which serve as semi-permeable passageways for the unclean blood. Fresh dialysate solution enters the dialyzer at its downstream end. The dialysate surrounds the straw-like tubes and flows through the dialyzer in the opposite direction of the blood flowing through the tubes. Fresh dialysate collects toxins passing through the straw-like tubes by diffusion and excess fluids in the blood by ultra filtration while leaving the red cells in the blood stream, which cannot pass through the straw-like tubes due to physical size.
For patients undergoing hemodialysis treatment, it is typical to monitor the patient's blood using a blood monitoring system during the treatment. For example, an optical blood monitoring system may be used that employs optical techniques to non-invasively measure, in real-time, the hematocrit level of blood flowing through the hemodialysis system. In such a system, a blood chamber may be attached in-line to the extracorporeal tubing—usually on the arterial side of the dialyzer. The blood chamber provides a viewing point for optical sensors during the hemodialysis procedure. Wavelengths of light are directed through the blood chamber and the patient's blood flowing there through, and one or more photo detectors can be used to detect the resulting intensity of each wavelength. From the detected light intensity, a hematocrit value can be calculated and a hemoglobin level can be estimated.